1. Field of the Invention
This invention relates to a method for bonding a color separation filter. More particularly, it relates to a method for bonding a color separation filter to a solid state image pick-up device.
2. Description of the Prior Art
A color filter of color separability has been used more frequently than ever together with a solid state image pick-up device which is used in place of the camera tube of the prior art as an element for converting two-dimensional image to the electrical signals, particularly in recent years with the progress in semiconductor production techniques. For example, a solid state image pick-up device called under the name of CCD (charge coupled device), MOS (metal oxide semiconductor) or BBD (bucket brigade device) houses a number of minutely divided imaging areas and driving circuits for taking out information from these imaging areas in one chip, and a color camera employing a solid state image pick-up device takes out color signals by means of color separation filters such as respective filter elements of red, green and blue which are arranged in the shape of a mosaic or stripes so as to confront the respective picture elements of a solid state image pick-up device such as CCD, MOS and BBD. At present, most of the color separation filters are generally bonded to the substrate of the imaging elements as mentioned above or display elements.
As the resin to be used for such bonding, a thermosetting type resin or UV-ray curable type resin may be used. However, in the case of bonding between a solid state image pick-up device and a color separation filter, it is necessary to realize a bonding agent thickness of 10 .mu.m or less and an alignment precision of about 1 .mu.m. When bonding is to be effected with such a precision, a thermosetting type resin, which undergoes curing gradually, cannot give good alignment precision. Further, productivity is worsened when the curing time is longer.
On the other hand, in the case of a UV-ray curable type bonding agent, by use of an aligner device, it is possible to effect registration between, for example, the picture element portion of solid state image pick-up device and the color separation filter with good precision, and by irradiation of UVray immediately after completion of registration, the bonding agent can be cured within a short period of time.
Also, when a UV-ray curable bonding agent is employed, for the purpose of effective utilization of an aligner device, partial curing of the bonding agent may be effected for a short time after setting the solid state image pick-up device and color separation filter on the aligner device, followed by full curing for a long time after dismantling from the aligner device, as proposed in Japanese Laid-open Patent Publication No. 2674/1981. However, there are also involved problems in UV-ray curable type bonding agents. That is, even in the region in which a stripe or mosaic pattern of color separation filters is formed, the transmission factor of UV-ray differs depending on the color of the filters as shown in FIG. 1, whereby it takes a long time until the bonding agent on the color separation filter as a whole is cured. Accordingly, if it is desired to shorten the curing time, the intensity of irradiation of UV-ray may be increased. Such an increase of intensity, however, will give rise to the problems of deterioration of dyes in the color separation filters. Besides, if the irradiation intensity of UV-ray is increased, since the UV-ray transmission factor at the blue filter element portion of the color separation filter is by far greater than that at the red or green filter element portion, strong UV-ray will be transmitted through the filter to harden abruptly the bonding agent beneath the blue filter element portion. As the result, volume shrinkage of the bonding agent accompaning with the curing will also occur abruptly, whereby uncured bonding agent surrounding the cured bonding agent will flow into the abruptly cured bonding agent to reduce the amount of the surrounding bonding agent. Consequently, when curing of the surrounding bonding agent has been completed, its thickness becomes smaller than that beneath the blue filter element portion to give rise to the problem that air corresponding to the reduction in thickness is included. Inclusion of the air will result in extreme lowering of color separation capacity at said portion.